Effect of gas composition and bias voltage on the structure and properties of a-C:H/SiO2 nanocomposite thin films prepared by plasma-enhanced chemical-vapor deposition

Abstract

The effects of gas flow rate ratio and bias voltage on the structure and properties of a-C:H and SiO2 nanocomposite thin film are investigated. The film depositions are performed in a 13.56 MHz, rf driven asymmetric plasma reactor using a mixture of styrene as the source gas for a-C:H, tetraethylorthosilicate (TEOS) as the source gas for SiO2, and hydrogen as a diluent. The structure and properties of the films are evaluated by ellipsometry, Fourier transform infrared (FTIR), Rutherford backscattering spectrometry stress gauge, and ultraviolet-visible spectrometer. The growth rate of the film appears to follow Langmuir–Hinshelwood kinetics. The film structure evaluated by FTIR shows that the nanocomposite film has characteristic peaks of a-C:H and SiO2 components. From the overlapped bands of Si–O and C–O stretching modes, it is deduced that SiO—C bonds are formed in the film via ion-assisted reactions. As the fraction of TEOS flow rate is increased, the refractive index, intrinsic stress, and graphitization of the film decrease, while the transparency of the film in the visible region increases. As the negative bias voltage at the substrate is increased during the film deposition, the refractive index, intrinsic stress, and graphitization increase, while the growth rate and the hydrogen content of the film decrease.